Method and apparatus for electrically heating a subsurface formation

ABSTRACT

A method and apparatus include providing one or more vertically spaced electrodes in the borehole in electrical contact with the formation. Two electrodes in a common borehole may be connected to a surface source of alternating current voltage to conductive paths provided respectively by a conductive casing and a conductive tubing suitably insulated from each other; or the two electrodes connected to the voltage source may be placed in separate adjacent boreholes. The flow of current through the formation is guided or directed by means of insulating barriers which extend laterally into the formation from the borehole in vertically spaced relation to the electrode.

United States Patent [72] Inventor Fred L. Crowson Portland, Tex. [2]]Appl. No. 29,954 [22] Filed Apr. 20, 1970 I451 Patented Nov. 16, 1971[73] Assignee The Electrothermic Co.

Corpus Christi, Tex.

[54] METHOD AND APPARATUS FOR ELECTRICALLY HEATING A SUBSURFACEFORMATION 22 Claims, 3 Drawing Figs.

[52] U.S. Cl 166/248, 166/60 [51] lnt.Cl E2lb43/24 [50] Field of Search166/248, 272, 285, 294, 295, 302, 57, 60, 306, 292

[56] References Cited UNITED STATES PATENTS 2,368,424 1/1945 Reistle, Jr166/292 X 3,106,244 10/1963 Parker 166/248 3,120,263 2/1964 Hoyt..166/306 X 3,137,347 6/1964 Parker 166/248 Primary Examiner-Stephen .l.Novosad Attorney-Giles Clegg, .lr.

ABSTRACT: A method and apparatus include providing one or morevertically spaced electrodes in the borehole in electrical contact withthe formation. Two electrodes in a common borehole may be connected to asurface source of alternating current voltage to conductive pathsprovided respectively by a conductive casing and a conductive tubingsuitably insulated from each other; or the two electrodes connected tothe voltage source may be placed in separate adjacent boreholes. Theflow of current through the formation is guided or directed by means ofinsulating barriers which extend laterally into the formation from theborehole in vertically spaced relation to theslest ast.

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sum 3 OF 3 AC OURCE J 92 INVENTOR FRED ROWSO AT1OHNEY METHOD ANDAPPARATUS FOR ELECTRICALLY HEATING A SUBSURFACE FORMATION BACKGROUND OFTHE INVENTION This invention relates to a method and apparatus forheating an oilor mineral-bearing formation to stimulate the flow of theoil or mineral; and more particularly to a method and apparatus forguiding the flow of electric current in the oilor mineral-bearingformation.

It is estimated that a large percentage of the known petroleum reservesin the United States cannot be recovered using conventional pumpingmethods. Known methods for effecting secondary recovery includetechniques known as water flood, steam injection and fire flood. All ofthese techniques require extensive and quite expensive surfaceinstallations for their implementation.

An object of this invention is to provide an improved method andapparatus for the recovery of oil or minerals through the use ofelectric current for heating the formation to encourage the flow of theoil or mineral from the formation.

Another object of this invention is to provide a simple and efficientmethod and apparatus for electrically heating the formation includingmeans for guiding the path of current flow through the formation.

The method according to the invention includes providing at least oneelectrode in the bore hole of the producing well in electrical contactwith the formation, providing a first conductive path in the bore holecontacting the electrode, providing a second conductive path from thesurface to the formation, providing a fiow of electrical current throughsaid conductive paths and through said formation to heat the formation,and provide insulating barriers extending into the formation from theproducing bore hole positioned relative to the electrode to guide theflow of current through the formation.

The apparatus of the invention includes at least one electrode in theproducing bore hole in contact with the formation, means within the borehole defining a first conductive path from the surface to the electrode,means defining a second conductive path from the surface to theformation, which second conductive path may include a second electrodein the producing bore hole or in another bore hole, a source ofalternating current voltage connected to the two conductive paths at thesurface to effect the flow of current through said conductive paths andsaid formation, and means defining one or more insulating barriersextending laterally from the bore hole in spaced relation to theelectrodes to guide the flow of current within the formation.

DRAWINGS The novel features of the invention, as well as additionalobjects and advantages thereof, will be understood more fully from thefollowing description when read in connection with the accompanyingdrawings in which:

FIG. I is a diagrammatic illustration of one form of the inventionincluding one electrode, one insulating barrier, and two conductivepaths in a common bore hole;

FIG. 2 is a diagrammatic illustration of another form of the inventionincluding one electrode, two insulating barriers, and a singleconductive path in the common bore hole; and

FIG. 3 is a diagrammatic illustration of still another form of theinvention including two electrodes, a single insulating barrier, and twoconductive paths in a common bore hole.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, thereis illustrated in FIG. 1 the lower portion of a producing well bore holewhich extends downwardly through the overburden 11, through theproducing formation 12, and terminates at the boundary between theproducing formation 12 and the underburden 13. A casing for the borehole extends from the surface and into the producing formation 12 to adepth somewhat below the upper surface of the formation, the casingincluding an upper conductive portion 14, which may be conventionalsteel casing for example,

and a lower insulating portion 15 which may be fabricated of fiberglassor ceramic for example. The upper conductive portion extends to a depthsomewhat above the producing formation 12.

A lower portion 16 of the bore hole 10 may be of reduced diameter, beingproduced through coring, for example, to ascertain the nature of theproducing formation. The bottom of the bore hole may be provided with acement plug 17 to support a conventional steel screen 18 provided withslots or other openings to permit the flow of oil into the well. Aninsulating packer 19 positions the screen relative to the lower end ofthe insulating casing 15 and physically seals the annular openingbetween the upper end of the screen and the lower end of the conductivecasing.

A string of tubing 21 extends from the surface to the bottom of the borehole, terminating within the screen 18, to carry the oil to the surface.This tubing is of conductive material to provide a path for the flow ofelectric current from the surface to one or more electrodes within thebore hole contacting the producing formation 12. An electrode 22 isdefined within two annular cavities 23 and 24 which are cut into theformation 12, extending laterally from the lower portion 16 of a borehole 10. These cavities, and the annulus between the walls of the borehole portion 16 and the exterior surface of the screen 18, are filledwith electrically conductive particles 25 which may be metallic pelletsof steel or aluminum, carbon pellets, or metallic pellets coated withcarbon, for example. These particles are retained in the cavities by theconductive screen 18 and the packer 19. The conductive tubing 21 iselectrically connected to the screen 18 by a pair of conventionalcentralizers 26 fixed to the tubing and having bands which bow outwardlyinto engagement with the inner walls of the screen.

As illustrated diagrammatically, a source of alternating cur rentvoltage 29 has one terminal connected to the upper end of the conductivetubing 12 and another terminal connected to the upper end of theconductive casing 14. Current flows then from the voltage source 29through the tubing 22, the centralizers 26, the screen 18 and theconductive particles 25 into the formation 12, then through theformation I2 and the overburden 11 and returning through the conductiveportion 14 of the casing. To prevent any short circuit current paths,the tubing 22 is insulated from the conductive casing l4 by means ofvertically spaced insulating spacers 27; and the screen 18 is insulatedfrom the conductive casing by the intervening nonconductive casingportion 15.

In order to increase the extent of the formation 12 which may beeffectively heated by the above described electrical circuit, the flowpath of current through the formation 12 may be guided to extend furtherin a radial direction from the bore hole 10. For this purpose, aninsulating barrier 30 is provided, consisting of generally disc-shapedshield of insulating material which extends radially from the bore holeand having an effective radius greater than that of the electrode. Thisbarrier is formed by providing a notched interval 31 in the insulatingportion 15 of the casing and in the adjacent cement, and forming anadjacent annular cavity 32 in the formation 12 of the desired radialextent. The notched interval and cavity are then filled with aninsulating material 33, such as an insulating cement or an insulatingepoxy, with the insulating material being retained by an insulatingsleeve 34 confined between the packer l9 and an upper packer 35.

FIG. 2 is a diagrammatic illustration of another form of producing wellbore hole 40 which includes a single electrically conductive path to anelectrode within the producing formation which is included in anelectric circuit including a second conductive path to the formation andwhich is spaced laterally from the bore hole 40, possible in an adjacentwell bore hole which may or may not be another producing well. In thisarrangement, the well bore hole extends from the surface through theoverburden '1 l and the producing formation 12 to the lower boundarybetween the producing formation 12 and the underburden 13. The bore holeincludes a lower cored portion 41, similar to the bore holeof FIG. I.This bore hole is cased, for example, with an insulating casing 42 whichextends from the surface to a point below the upper surface of theproducing formation 12; and a screen 43 is positioned in the lower borehole portion 41 and physically connected to the lower end of the casing42 by means of a packer 44.

A low resistance electrically conductive path is provided from thesurface to the bottom of the bore hole by a string of conductive tubing45 which is also the production tubing for carrying the production fluidto the surface.

An electrode 47 is identical to that of FIG. 1 including centralizers 48affixed to the lower end of the tubing and contacting the screen 43; thescreen 43 retaining conductive particles 49 with upper and lower annularcavities 50 and 51 extending laterally from the bore hole portion 41,with the screen maintaining electrical contact with these particles.

With the arrangement of FIG. 2, an alternating current voltage source53, at the surface, has one terminal connected to the upper end of thetubing 45, and another terminal connected at the surface through aconductor 54 to the upper end of a conductive path defining tubing orrod extending toward the formation in an adjacent bore hole, forexample. The flow of current then is through the tubing 45 centralizer48 screen 43 particles 49, and through the producing formation 12 to theother conductive path defining means.

The conductive tubing 45 is insulated from the walls of the bore hole,above the formation, by the insulating casing 42. Since the bore hole 40contains only a single conductive path, and since the conductive tubingis a much lower resistance path than would be the walls of theformation, it may not be necessary to provide particular means toinsulate the tubing from the bore hole walls of the formation 12 in thisconfiguration. Accordingly, the casing may, in the alternative, consistof an upper conductive portion and a lower insulating portion as in thearrangement of FIG. 1.

It may be desirable, in this situation, to prevent too rapid a verticaldiffusion of the current flow path as it moves away from the electrode47, in order to concentrate the power absorption of the electricalcurrent and therefore the heating effect within an effective areaadjacent to the producing well bore.

To prevent the too rapid diffusion of the current fiow path through theformation 12 adjacent to the electrode 47, there are provided twoinsulating barriers or shields 55 and 56 disposed respectively above andbelow the electrode 47. The upper barrier 55 is similar to thatillustrated in FIG. 1 consisting of a disclike mass 57 of insulatingmaterial disposed in a notched interval 58 in the lower end of theinsulating casing 42 and an adjacent cavity 49. The insulating cement orepoxy 57 is again retained by an insulating sleeve 60 confined between alower packer 44 and an upper packer l. The lower insulating barrier 56is defined by a disclike mass 62 of insulating cement or epoxy, forexample, which defines the bottom of the bore hole portion 41 and whichextends laterally from the bore hole in an annular cavity 63.

The radial extent of the insulating barriers 55 and 56 is preferablygreater than that of the electrode 47.

FIG. 3 is a diagrammatic illustration of still another producing wellarrangement wherein electric current flows between electrodes verticallyspaced in a common bore hole, and a bore hole containing means definingseparate conductive paths for the respective electrodes. Referring toFIG. 3, there is shown a production bore hole 70 extending from thesurface through the overburden 11 and the producing formation 12 to theboundary between the producing formation and the underburden 13. In thisconfiguration, the bore hole is cased from the surface to the bottomthereof, with an upper insulating portion 71 extending from the surfaceto a point below the upper surface of the producing formation 12, andwith an insulating portion 72 extending from the conductive portion tothe bottom of the bore hole. Preferably, the casing is cemented in thebore hole with an insulating cement, at least in the portion of the borehole which extends through the producing fonnation 12. The insulatingcement may also define a base or bottom plug for the bore hole 70.

A conductive tubing 75 for carrying the produced fluid to the surfacealso defines a low-resistance-conductive path for a lower electrode 76disposed adjacent to the bottom of the bore hole. This lower electrodeconsists of a mass of conductive particles 77, such as metalliccarbon-coated pellets, disposed in a notched interval in the lower endof the insulating casing 72 and adjacent cement 73, and an adjacentcavity 78 in the producing formation 12. The particles are retained inthe cavity by a conductive sleeve or screen 79, positioned in the bottomof the bore hole by a packer 80, the sleeve 79 being electricallyengaged by a conductive centralizer 81 fixed to the lower end of thetubing 75.

An upper electrode 84 is positioned adjacent to the upper surface of theproducing formation 12 and consists of a mass of conductive particles 85confined within a notched interval provided in the lower end of theconductive casing 7 l and the adjacent cement and in an adjacent annularcavity 86 extending into the formation 12. The particles are retainedwithin a cavity by a conductive sleeve 87, confined between a lowerinsulating packer 88 and an upper packer 89.

The conductive casing 71 defines a conductive path from the surface tothe electrode 84, and must be insulated from the conductive tubing 75.This insulation is provided by a string of insulating tubing 91 whichextends from the surface to a depth sufficient to overlap the upper endof the insulating casing 72. The insulating packer 88 mechanicallycouples these insulating members, and seals the annulus between them toobviate any conductive path between the electrodes 76 and 84 within thecasing. Similarly, the insulating casing 72 and the insulating cement 72obviate any low-resistance conductive path between the electrodes, sothat the current flowing between the electrodes necessarily flowsthrough the formation 12. The terminals of the alternating currentsource 92 are connected at the surface to the conductive tubing and theconductive casing so that the current flowsthrough the tubing andassociated electrode 76, through the formation 12, then through theelectrode 84 and associated conductive casing 7!.

In order to expand the area of the formation which is effectively heatedby the current flowing therethrough, an insulating barrier 93 is formedwithin the formation between the electrodes. This barrier takes the formof a disc-shaped mass of insulating material 94, such as insulatingcement or epoxy, confined in an annular cavity 95 formed in a formation12 through a notched interval 96 provided in the insulating casing 72and the adjacent cement 73. The insulating material is retained in acavity bymeans of an insulating sleeve 96 supported on a packer 97.

The insulating barrier 93 preferably has a radial extent greater thanthat of the electrodes 76 and 84, and serves to deflect the current flowpath through the formation outward relative to the bore hole to effectheating of the formation at radial distance greater from the bore holethan would otherwise be effected, and thereby increase the amount offormation which may be produced. The produced fluid flows from theformation into the well through perforations 98, formed in theinsulating casing and the adjacent cement by conventional techniques;and the production tubing 75 may include slots or other openings 99 toeffect the flow of fluid into the tubing to be transported to thesurface.

A method of the invention which may be practiced by the above describedproducing well configurations, or by other configurations, includes thesteps: establishing an electrode in the producing well bore hole inelectrical contact with the formation to be produced; providing a firstlow-resistance conductive path contacting the electrode, which ispreferably provided by a conductive tubing which is also the tubing fortransporting the produced fluid to the surface; providing a secondlow-resistance conductive path from the surface to the formation, whichmay be provided by a conductive path from the surface to the formation,which may be provided by a conductive casing either alone or inconjunction with a second electrode, or a conductive pipe or rod in anadjacent bore hole; producing a flow of electric current through the twoconductive paths and the formation. The current being carried in themation to provide more efficient or more extensive heating of 5 theformation.

What is claimed is:

1. A method for electrically heating a subsurface formation through atleast one bore hole extending from the surface into said formationincluding the steps:

establishing an electrode in said bore hole in electrical communicationwith said formation;

providing a first relatively low-resistance conductive path in said borehole extending from the surface to contact said electrode; providing asecond relatively low-resistance conductive path extending from thesurface to said formation;

producing a flow of electric current from a voltage source through saidfirst and second conductive paths, said electrode, and said formation toheat said formation;

providing at least one insulating barrier extending laterally from saidbore hole in vertically spaced relation to said electrode to guide thefiow path of electric current through said formation.

2. A method as set forth in claim 1 including providing said insulatingbarrier by producing an annular cavity extending laterally into saidformation from said bore hole;

and filling said cavity with an insulating material 3. A method as setforth in claim 2 wherein said cavity is filled with an insulatingcement.

4. A method as set forth in claim wherein said cavity is filled with aninsulating epoxy.

5. A method as set forth in claim 1 including providing an insulatingliner for said bore hole extending between said electrode and saidbarrier.

6. A method as set forth in claim 1 including providing two insulatingbarriers extending laterally into said formation from said bore hole andpositioned respectively above and below said electrode.

7. A method as set forth in claim 6 including providing said secondconductive path within a bore hole spaced laterally from said firstnamed bore hole.

8. A method as set forth in claim 1 including establishing a secondelectrode in said bore hole in electrical communication with saidformation and in vertically spaced relation to said first namedelectrode; connecting said second electrode to said second conductivepath; insulating said first and second electrodes from each other withinsaid bore hole;

and providing said insulating barrier between said vertically spacedelectrodes.

9. A method as set forth in claim 8 including providing an insulatingliner in said bore hole between said electrode;

and joining said insulating barrier to said insulating liner.

10. A method as set forth in claim 9 and providing said insulatingbarrier by fon'ning a notched interval in said insulating liner,providing an adjacent annular cavity in said formation, and filling saidnotched interval and said cavity with an insulating material.

11. A method as set forth in claim 1 including providing a conductivetubing in said bore hole defining said first conductive path;

and providing a conductive casing in said bore hole defining said secondconductive path.

12. A method as set forth in claim 1 including providing an insulatingbarrier above said electrode;

and providing said second conductive path within said bore holeterminating at point above said insulating barrier.

13. A method as set forth in claim 12 including providing a conductivetubing defining said first conductive path;

providing a conductive casing defining said second conductive path;

and insulating said conductive tubing from said conductive casing.

14. Apparatus for electrically heating a subsurface formation through atleast one bore hole extending from the surface into said formationcomprising:

means defining an electrode in said bore hole communicating with saidfonnation;

means in said bore hole defining a first relatively low-resistanceconductive path extending from the surface to said formation andconnected to said electrode;

means defining a second relatively low-resistance conductive pathextending from the surface to said formation;

a source of alternating current supply voltage;

means at the surface connecting one terminal of said voltage source tosaid first conductive path, and means con necting another terminal ofsaid voltage source to a second conductive path for completing anelectric circuit through said first and second conductive paths and saidelectrode through said formation;

and means defining at least one insulating barrier extending laterallyfrom said bore hole into said formation; said barrier means being spacedvertically from said electrode to guide the flow of current through saidformation.

15. Apparatus as set forth in claim 14 wherein said insulating barriermeans is defined by a mass of insulating material urged into an annularcavity extending laterally from said bore hole. 16. Apparatus as setforth in claim 15 wherein said insulating material is an insulatingcement. 17. Apparatus as set forth in claim 15 wherein said insulatingmaterial is an epoxy material. 18. Apparatus as set forth in claim 14said first conductive path being defined by a conductive tubing; andsaid second conductive path being defined by a conductive casing.

19. Apparatus as set forth in claim 14 said insulating barrier beingdisposed vertically above said electrode; and said second conductivepath being disposed within said bore hole, terminating at a point abovesaid insulating barrier.

20. Apparatus as set forth in claim 14 first and second insulatingbarriers disposed respectively above and below said electrode; saidsecond conductive path being provided in a bore hole spaced laterallyfrom said first named bore hole.

21. Apparatus as set forth in claim 14 means defining first and secondvertically spaced electrodes; said first electrode being connected tosaid first conductive path; said second conductive path being disposedwithin said bore hole and being connected to said second electrode;

said insulating barrier being disposed vertically between said first andsecond electrodes.

22. Apparatus as set forth in claim 21 means defining an insulatingliner for said bore hole between said first and second electrodes; andsaid insulating barrier extending laterally from said insulating liner.

1. A method for electrically heating a subsurface formation through atleast one bore hole extending from the surface into said formationincluding the steps: establishing an electrode in said bore hole inelectrical communication with said formation; providing a firstrelatively low-resistance conductive path in said bore hole extendingfrom the surface to contact said electrode; providing a secondrelatively low-resistance conductive path extending from the surface tosaid formation; producing a flow of electric current from a voltagesource through said first and second conductive paths, said electrode,and said formation to heat said formation; providing at least oneinsulating barrier extending laterally from said bore hole in verticallyspaced relation to said electrode to guide the flow path of electriccurrent through said formation.
 2. A method as set forth in claim 1including providing said insulating barrier by producing an annularcavity extending laterally into said formation from said bore hole; andfilling said cavity with an insulating material
 3. A method as set forthin claim 2 wherein said cavity is filled with an insulating cement.
 4. Amethod as set forth in claim wherein said cavity is filled with aninsulating epOxy.
 5. A method as set forth in claim 1 includingproviding an insulating liner for said bore hole extending between saidelectrode and said barrier.
 6. A method as set forth in claim 1including providing two insulating barriers extending laterally intosaid formation from said bore hole and positioned respectively above andbelow said electrode.
 7. A method as set forth in claim 6 includingproviding said second conductive path within a bore hole spacedlaterally from said first named bore hole.
 8. A method as set forth inclaim 1 including establishing a second electrode in said bore hole inelectrical communication with said formation and in vertically spacedrelation to said first named electrode; connecting said second electrodeto said second conductive path; insulating said first and secondelectrodes from each other within said bore hole; and providing saidinsulating barrier between said vertically spaced electrodes.
 9. Amethod as set forth in claim 8 including providing an insulating linerin said bore hole between said electrode; and joining said insulatingbarrier to said insulating liner.
 10. A method as set forth in claim 9and providing said insulating barrier by forming a notched interval insaid insulating liner, providing an adjacent annular cavity in saidformation, and filling said notched interval and said cavity with aninsulating material.
 11. A method as set forth in claim 1 includingproviding a conductive tubing in said bore hole defining said firstconductive path; and providing a conductive casing in said bore holedefining said second conductive path.
 12. A method as set forth in claim1 including providing an insulating barrier above said electrode; andproviding said second conductive path within said bore hole terminatingat point above said insulating barrier.
 13. A method as set forth inclaim 12 including providing a conductive tubing defining said firstconductive path; providing a conductive casing defining said secondconductive path; and insulating said conductive tubing from saidconductive casing.
 14. Apparatus for electrically heating a subsurfaceformation through at least one bore hole extending from the surface intosaid formation comprising: means defining an electrode in said bore holecommunicating with said formation; means in said bore hole defining afirst relatively low-resistance conductive path extending from thesurface to said formation and connected to said electrode; meansdefining a second relatively low-resistance conductive path extendingfrom the surface to said formation; a source of alternating currentsupply voltage; means at the surface connecting one terminal of saidvoltage source to said first conductive path, and means connectinganother terminal of said voltage source to a second conductive path forcompleting an electric circuit through said first and second conductivepaths and said electrode through said formation; and means defining atleast one insulating barrier extending laterally from said bore holeinto said formation; said barrier means being spaced vertically fromsaid electrode to guide the flow of current through said formation. 15.Apparatus as set forth in claim 14 wherein said insulating barrier meansis defined by a mass of insulating material urged into an annular cavityextending laterally from said bore hole.
 16. Apparatus as set forth inclaim 15 wherein said insulating material is an insulating cement. 17.Apparatus as set forth in claim 15 wherein said insulating material isan epoxy material.
 18. Apparatus as set forth in claim 14 said firstconductive path being defined by a conductive tubing; and said secondconductive path being defined by a conductive casing.
 19. Apparatus asset forth in claim 14 said insulating barrier being disposed verticallyabove said electrode; and said second coNductive path being disposedwithin said bore hole, terminating at a point above said insulatingbarrier.
 20. Apparatus as set forth in claim 14 first and secondinsulating barriers disposed respectively above and below saidelectrode; said second conductive path being provided in a bore holespaced laterally from said first named bore hole.
 21. Apparatus as setforth in claim 14 means defining first and second vertically spacedelectrodes; said first electrode being connected to said firstconductive path; said second conductive path being disposed within saidbore hole and being connected to said second electrode; said insulatingbarrier being disposed vertically between said first and secondelectrodes.
 22. Apparatus as set forth in claim 21 means defining aninsulating liner for said bore hole between said first and secondelectrodes; and said insulating barrier extending laterally from saidinsulating liner.